Project Summary/Abstract Underuse of clinically effective medications among minority adults in midlife may contribute to racial and ethnic disparities in chronic disease related morbidity and mortality in late life. Medication affordability has been identified as an important driver of disparities in treatment adherence and recent trends in employer-sponsored prescription drug coverage toward increased patient cost sharing (e.g., copays) have the potential to exacerbate these disparities. Yet, there is a paucity of strong research evidence on the effects of out-of-pocket (OOP) drug costs on disparities in treatment adherence over the life course. In a prior study, we found evidence of a complex relationship between OOP drug costs and adherence which likely differs by race and ethnicity over time. For example, as patients age and OOP costs increase due to higher drug burden, patients may become more sensitive to cumulative drug costs regardless of race or ethnicity. In addition, potentially modifiable factors at the provider (e.g., prescribing habits) and health system level (e.g., refill complexity) may interact with OOP drug costs in ways that exacerbate adherence disparities in midlife. However, our prior study could not adequately explore these complex and interacting factors. The primary objective of this competing renewal is to estimate the effect of OOP drug costs on disparities in medication adherence among middle-aged adults (40-64) within a large integrated health care setting (>4 million members) offering a wide variety of drug benefits and consistent access to primary care. We hypothesize that the relationship between OOP drug costs and racial and ethnic differences in adherence will be modified by age. In addition, we will examine potential interactions between OOP drug costs and modifiable factors at the provider and health system level that may amplify disparities in adherence. Focusing on patients with cardiometabolic conditions (i.e., hypertension, diabetes) and select medication classes (e.g., lipid lowering, antihypertensives, antidiabetes), we will leverage a rich longitudinal electronic medical record and employ rigorous statistical methods to estimate the effect of OOP drug costs on medication adherence overall and by race and ethnicity, including examining age-specific effects and interactions between OOP drug costs and modifiable factors at the provider and health system level. In addition, we will identify aids and barriers to integrating health equity as a measurable criterion for evaluating drug benefit designs and relevant contextual factors from the perspective of decision makers (e.g., employers, health plans, pharmacy benefit managers). If successful the proposed study has the potential to inform the design of drug benefits that simultaneously promote clinical effectiveness and equitable health care outcomes.